The invention relates to a method and a system for monitoring insulation faults in an electric network supplied by at least one electric power source and a vehicle comprising an insulation fault monitor.
In hybrid electric vehicles, the “high-voltage” electric system is isolated from vehicle chassis (“floating ground”). If a person touches, for example, the positive pole of the DC-bus, there will not be a risk for electric shock. However, if there is an insulation fault in the “high-voltage” electric system, i.e. one of the electric poles comes into contact with the vehicle chassis, there is a risk for electric shock if a person gets in contact with the other pole.
It is known in the art to provide an insulation resistance monitor in the battery that monitors the insulation resistance so that the control system can de-energize the electric system to avoid risk for electric shock. For instance JP 2005127821 A and JP 08294225 A disclose an insulation resistance monitor.
U.S. Pat. No. 6,952,103 B2 discloses an insulation resistance monitor and a method for detecting insulation faults on an electrically driven vehicle. In order to sense the resistance between the battery terminals and the ground potential, a measuring circuit is provided comprising three switches. A test sequence is employed for testing the insulation resistance monitor before monitoring insulation faults in the vehicle. Only if the test sequence is passed successfully, the measurement of the insulation resistance is performed.
Usually, the insulation resistance monitor is connected in parallel with the battery cells, behind the battery disconnect breakers. When driving e.g. a hybrid electric vehicle, rotating electric machines with permanent magnets will create hazardous voltages in the electric circuit connected to the electric machine and the inverter (power electronics). Thus, if the battery breakers are opened, it will not be possible to measure any insulation resistance outside of the battery breakers, i.e. outside of the battery enclosure.
In some circumstances, e.g. battery faults like battery over-temperature, abnormal cell voltage distribution, etc., in known systems the battery will be disconnected from the “high-voltage” electric system. When the battery is disconnected, the insulation resistance monitor connected to the battery is not be able to monitor the insulation resistance in the energized circuit outside of the battery enclosure.
It is desirable to provide a method to provide insulation resistance monitoring even if an electrical power source is disconnected. It is also desirable to provide a vehicle employing a method for insulation resistance monitoring.
A method is proposed for monitoring an insulation fault in an electric network with at least one electric power system supplying electric power to one or more electric loads, and at least one insulation resistance monitor, wherein the at least one electric power system comprises at least one electric power source, and wherein the at least one insulation resistance monitor monitors an insulation resistance between terminal leads of the at least one electric power source and at least one reference potential. The method comprises the steps of (i) disconnecting the at least one electric power source from the one or more loads by opening each terminal lead; (ii) measuring the insulation resistance between the electric circuit of at least one electrical power source and the reference potential; (iii) measuring the insulation resistance for the total electric network, preferably between the at least one electrical power source and the reference potential, (iv) closing one terminal lead with the other terminal lead open and (v) measuring the insulation resistance (R_isol2) for the total electric network.
Favourably, the electrical current provided by the at least one electric power source is disabled as long as one terminal lead is open. Particularly, opening a terminal lead can be achieved by opening one or more breakers arranged in the terminal lead. The invention can be employed with electric power sources such as energy storage units, such as batteries, ultra-capacitors, as well as fuel cell units. By opening both terminal leads, the insulation resistance of the electric power source itself can be tested. If no fault is detected, no insulation fault is injected into the energized electric system from the electric power source. Further, the risk that the measured isolation resistance is deteriorated by a very low internal resistance can be eliminated. If an insulation fault is detected, it can be decided if the electrical power source is to be shut down or the system is to be used without an insulation resistance monitor. Advantageously, the insulation resistance of the electric power source itself, when both terminal leads are opened, can be used to compensate for this insulation resistance in the measurement with a single terminal lead opened, thus increasing the accuracy of the measurement.
Further, various kinds of state-of-the art insulation resistance monitors can favourably employ the current invention. The invention provides a safe estimation of the insulation resistance. The invention provides a less costly solution compared to e.g. adding more insulation resistance monitors. Favourably, the insulation resistance can be measured on both poles of the electrical power source.
According to a favourable embodiment, the steps of (v) dosing the second terminal lead with the first terminal lead open; and (vi) measuring the insulation resistance for the total electric network are not performed if the isolation resistance is below a predefined threshold. For instance, it is required that the insulation resistance must be at least 300 kω for a voltage of 600 V dc. Not performing the steps can advantageously reduce the risk for an electric shock due to indirect contact. Further, this can reduce the risk for measurement deterioration of the measured isolation values for the disconnected parts of the electric system, i.e. without the electric power source.
Advantageously it is possible to compensate the measured insulation resistance of the total electric network for the insulation resistance between the electric circuit of at least one electrical power source and the reference potential in order to obtain the isolation resistance for the electric network without the disconnected electric power source.
According to a favourable embodiment, the electrical power source can be shut down when an insulation fault is detected when both terminals are open. Additionally or alternatively, an indication that no insulation resistance monitor is available can be issued when an insulation fault is detected when both terminals are open.
According to another favourable embodiment, at least one terminal can be opened periodically to provide monitoring of the insulation resistance. One of the breakers can also be closed continuously to provide isolation monitoring of the part of the electric that is located on the other side of the electric power source breaker. As long as one of the electric power source breakers, e.g. battery breakers, is open, it possible to have the other breaker closed in order to monitor the “disconnected” part of electric system.
According to another favourable embodiment, at least one terminal can be opened by opening a breaker arranged in the respective terminal. Preferably, at least one of the breakers can be surveyed with respect to its open/close operation. Preferably, a voltage over at least one breaker can be determined by measuring the voltage on each side of the particular breaker. By measuring the voltage on each side of the breaker a reliable diagnosis means of the breaker is available. Particularly, a voltage drop over at least one breaker can be determined by measuring the voltage on each side of the particular breaker. This measurement can be performed during and before the isolation testing. If this measurement shows that the breakers do not function properly (i.e. the voltage difference is large when both breakers are closed or if the voltage difference is too small when the any breaker is open), the breakers cannot be controlled as intended, and the isolation measurement procedure is interrupted in order to maintain the electric power source current interruption. Favourably it is possible to detect an insulation fault and distinguish on which terminal the fault occurs. By using breakers, it is as well possible to decide on which side of the breaker the fault occurs.
According to another favourable embodiment, opening and closing operations of the terminals can be controlled by an electronic control unit of the electric power source. However, the opening and closing operations can alternatively or additionally be controlled by some supervising control unit. Favourably, an indicator signal can be issued indicating if the particular breaker has a requested state or not. If this measurement shows that the breakers do not function properly, the breakers cannot be controlled as intended, and the isolation measurement procedure is interrupted in order to maintain the electric power source current interruption. For instance, indicator signal contacts can be integrated into the breaker, which are connected if the breaker is closed and which are not connected if the breaker is opened. If the voltage is measured on both sides of the electric power source breakers, it can be used to diagnose if the breakers are functioning as intended. If the breakers do not operate according to the algorithm, the electric power supply current cannot be interrupted and the isolation measurement cannot be performed.
According to another favourable embodiment, an audible and/or visible and/or haptic alarm is issued on detecting an insulation fault. Safe information of the user is provided.
According to another aspect of the invention, a vehicle comprising at least an electric propulsion system powered by at least one electric power system is proposed, wherein at least one insulation resistance monitor for monitoring an insulation fault in an electric network is coupled to the electric propulsion system, wherein the at least one electric power system comprises at least one electric power source, and wherein the insulation resistance is monitored by performing the method according to one of the features described above.
In the vehicle, the power system is preferably a high voltage system, e.g. providing several hundreds of volts, for providing power to an electric motor which can be used e.g. for propelling the vehicle. Other usages include electric power generation by the electric motor for charging the electric power supply or for power supply to the electric auxiliary loads. The electric power system must be insulated against ground potential, e.g. the car body. The insulation resistance must be higher than a specified resistance. In today's vehicles with an electric motor the insulation resistance must be at least 300 kω for a voltage of 600 V dc.
Preferably, the at least one electric power source can comprise at least one electrical storage device, for instance a battery or a super capacitor.
According to another favourable embodiment, the at least one electric power source can comprise additionally or alternatively at least one fuel cell device.
According to another favourable embodiment, at least one breaker can be provided for performing the monitoring of the insulation resistance. A breaker, also known as battery breaker, is a standard device used in high voltage batteries or other electric power sources. In a preferred embodiment, one breaker can be provided per terminal of the electric power source.
According to another favourable embodiment, the at least one breaker can be arranged inside a housing of the at least one electric power source. It is possible to provide one or more breakers outside the housing additionally or alternatively to an arrangement inside the housing.
According to another favourable embodiment, the at least one breaker can be coupled to an electric motor drive system. The electric motor drive system favourably can comprise a motor inverter to which the breaker can be coupled.
According to another favourable embodiment, the vehicle can be embodied as an electric vehicle. The electric vehicle can provide a purely electric drive system which can be powered by one or more batteries and/or one or more super capacitors.
According to another favourable embodiment, the vehicle can be embodied as a hybrid vehicle. The hybrid vehicle can provide at least one electric drive system in combination with another source of propulsion energy, such as a combustion engine or a combination of fuel cell and electric energy storage. The hybrid vehicle can be a parallel or a series hybrid.
Further, a computer program is proposed comprising a computer program code adapted to perform a method or for use in a method according to at least one of the method steps described when said program is run on a programmable microcomputer. Favourably, the computer program can be adapted to be downloaded to a control unit or one of its components when run on a computer which is connected to the internet. The control unit can be a control unit controlling the electrical power source or the electric power system or some supervising control unit in a vehicle in which the electric power system is employed.
Further, a computer program product stored on a computer readable medium is proposed, comprising a program code for use in a method according to at least one of the method steps on a computer.